What We Say
You can include the basics, or if you are clever you can try to be a bit more proactive too!
What kind of things do people include?
Conventionally, thank you letters are courteous, concise and relatively to the point. If you are dealing with a main contact it is traditional to address your letter to him/her, and thank him/her in person for everything.
Additionally, thank you letters are also an opportunity to add a bit of extra detail, or mention things that you perhaps forgot to mention at the interview. At the same time, you need to be careful about how you include these. If you can’t include them naturally, then it’s probably best to just omit them completely. After all, a thank you letter is a thank you letter. It is not a cover letter, CV or anything else. That said, the best writers have a knack of managing to say what needs to be said, but in a natural and fluent manner.